Switching circuit to control call number transmitters in automatic telephone systems

ABSTRACT

A SWITCHING CIRCUIT FOR USE IN CONJUNCTION WITH TELEPHONE SYSTEMS WHEREIN CALL NUMBER TRANSMITTERS ARE EMPLOYED TO AUTOMATICALLY ESTABLISH CONNECTIONS BETWEEN SELECTED SUBSCRIBERS. A SIGNAL RECEIVER IS RESPONSIVE TO THE RECEIPT OF SIGNALS, RATHER THAN THE REPETITION RATE THEREOF, TO PROVIDE CONTROL CRITERIA IN CONJUNCTION WITH THE SWITCHING STATE OF THE CALL NUMBER TRANSMITTER, TO CONTROL THE LATTER. THE CALL NUMBER TRANSMITTER IS THEREBY CONTROLLED TO INTERRUPT TRANSMISSION OF THE CALL NUMBER UPON RECEIPT OF A BUSY TONE BY THE SIGNAL RECEIVER, IN ORDER THAT THE CENTRAL CONTROL SYSTEMS ASSOCIATED WITH THE TELEPHONE EXCHANGE AND THE TRUNK ARE NOT SEIZED FOR AN UNNECESSARY PERIOD OF TIME AND ARE THEREFORE FREE FOR SEIZURE BY OTHER SUBSCRIBERS. THE TRANSMISSION OF THE FIRST DIGIT OF THE CALL NUMBER IS DEPENDENT UPON RECEIPT OF AN APPROPRIATE SIGNAL BY THE SIGNAL RECEIVER, RATHER THAN UPON THE ELAPSING OF A PREDETERMINED TIME PERIOD ASSOCIATED WITH SWITCHING THE FIRST DIAL STAGE OF THE ASSOCIATED EXCHANGE TO A CONDITION WHEREIN IT IS READY TO RECEIVE THE FIRST DIGIT.

United States Patent 1 3,5 3170 [72] Inventors Wolf Nottnagel; 3,211,838/1965 Ericsson. 1 179/27 A I No gi i Mumch Germany PrimaryExaminer-Kathleen H. Claffy g 14 1967 Assistant Examiner-Douglas W. OlmsPatented Jun: 28, 1971 Attorney-Birch. Swindler, McKie and Beckett [73]Assignee Siemens Aktiengesellschaft Berlin, Germany 3% Pnomy g 1966ABSTRACT: A switching circuit for use in conjunction with 1:5 1telephone systems wherein call number transmitters are em- 1 ployed toautomatically establish connections between selected subscribers. Asignal receiver is responsive to the [54] SWITCHING CIRCUIT o CONTROLCALL receipt of signals, rather than the repetition rate thereof, toNUMBER TRANSMrn-ERS 1N AUTOMATIC provide control criteria in conjunctionwith the switching state TELEPHONE SYSTEMS of the call numbertransmitter, to control the latter. The call number transmitter isthereby controlled to interru t trans- 6 Claims, 2 Drawmg Figs. P

mission of the call number upon receipt of a busy tone by the [52] U.S.II 179/27, signal receiver, i order h the central control sysmms 179/18sociated with the telephone exchange and the trunk are not se- [51] Int.Cl. 04m 3/00 ized for an unnecessary period f time and are th f f Fieldof Search 179/2702, for Seizure by other Subscribers The transmission fthe fi t 18 (3) digit of the call number is dependent upon receipt of anappropriate signal by the signal receiver, rather than upon the [56](defences Clted elapsing of a predetermined time period associated withUNITED STATES PATENTS switching the first dial stage of the associatedexchange to a 2,861,131 1 1/1958 Villmann 179/90 condition wherein it isready to receive the first digit.

LINE GROUP mama u m: 1 GROUP 11 GROUP LINE waii Hum SELECTOR mm my mornSELECTOR SELECTOR SELECTOR SUBSCRIBER I81 r T I REPEATOR I A82 IBW HEWLW SUBSCRIBER I l smmu I I U8 I AUG 1 I52 m2 snmom A51 CW COUPLINGSUBSCRIBER mom I I SYSTEM I We cm mmarn DWN TRANSMITTER l L J E SOUNDRECEIVER PATENTEDJUN281931 3,588,370

SUBCRIBER LINE GROUP REPEATOR H LINE IGROUP HGROUP um CIRCUIT FINDERSELECTOR m mgm FINDER SELECTOR SELECTOR SELECTOR SUBSCRIBER 151 r"IREPEATOR l ASZ IGW HEW LW mm m I Ue Me i TSZ m2 323%? A51 MICOUPUNGISUBSCRIBER CIRCUIT v 1 {SYSTEM RNG I CALL NUMBER I OWN L JTRANSMITTER Iscum) TE RECEIVER I R$W TN a? 5:31] REPEATER L V k k COUPLING SYSTEM kSHORTOA F KSP mmmswr @kkA' CONVERTER USP 3st no! 1 n J M x -11 STORAGESOUND RECEIVER CROSS REFERENCE TO RELATED APPLlCATlON Applicants claimpriority from corresponding German Pat. application Ser. No. $107,094,filed Nov. 24, 1966, in Germany.

EACEQG ROUND OF THE lNVENTlON 1. Field of the invention The inventionrelates to a switching system for long distance communications and hasparticular utility in telephone installations. A call number transmitterand a signal receiver are associated with a subscriber installationhaving extension stations to automatically establish connections betweenthe subscriber installation and a public telephone exchange, and tosupervise the operating state of the connection system.

2. Description of the Prior Art Prior art long distance communicationsystems provide for the supervision of the operating state of theconnection system associated with connection lines of a telephoneinstallation. Signal receivers are connected to the connection lines andare switched into operation during establishment of the connectionbetween the calling and called subscriber stations, during the timeinterval prior to transmission of the first current pulse seriesrepresentative of the first digit of the call number by the callingstation, and/or within the time interval between succes sive currentpulse series representative of successive digits of the call number.Therefore receipt of audible tone signals that may be indicative of dialtones, ring back tones, or busy tones by the signal receiver,representative of the state of the connection system during the timethat the desired connection is being established, is possible. Byevaluating the received tones and, more particularly, the repetitionrate thereof, corresponding switching criteria may be derived to controlthe call number transmitter.

The call number transmitter may be adapted to operate as a call repeaterso that upon the receipt of a busy tone by the signal receiver, the callis repeated until the signal receiver receives a ring baclt toneindicating that the called subscriber is free. The call may then becompleted.

Modern telephone systems, however, operate at high switching speedsthrough the use of electronic switching systems. Therefore, the callnumber transmitter is subjected to demands corresponding to therelatively high switching speeds, and the prior art circuits describedabove cannot satisfy such demands, without expensive changes in theircir cuitry. Thus the call number transmitters of prior art systemsrequire control times set by the evaluation time associated withreceived dial tones. Further, in prior art systems, the first pulseseries representative of the first digit of the call number isautomatically transmitted only when the first dial stage of theassociated exshange station is switched to a position wherein it isready to receive it; otherwise, erroneous dialing could occur.

The time associated with switching the first dial stage of associatedexchange system differs, depending upon the type of telephone systememployed and the traffic therethrough, and it is therefore not practicalto set a uniform predetermined time period before the call numbertransmitter transmits the first digit. Therefore, it is particularlyadvantageous to make transmission of the first pulse series dependentupon receipt by the signal receiver of a dial tone, rather than upon theelapsing of a predetermined time period associated with switching thefirst dial stage to a condition wherein it is ready to receive the firstdigit. Further, ifa busy signal is received by the signal receiver, thecall number transmitter should im mediately be controlled to interrupttransmission of the call number, in order that the central controlsystems associated with the exchange and the trunk are not seized for anunnecessary period of time and are therefore freed for seizure by othersubscribers. The prior art systems described above do not satisfy thesecriteria because the time associated with evaluating the repetitionrates of signals received by the signal receiver is too long.

SUMMARY OF THE lNVlENTllON These and other disadvantages and defects ofprior art systems are solved by the present invention which eliminatesthe relatively long time periods associated with evaluating signalsreceived by the signal receiver to control the call number transmitter.A switching circuit is employed in conjunction with the call numbertransmitter and signal receiver that is connected to the connectionlines between selected subscribers to provide criteria indicative of theresponse of the signal receiver to received signals and the condition ofthe call number transmitter, to control the initiation as well as theinterruption of transmission of the call number by the call numbertransmitter. The switching state of the signal receiver produced inresponse to received signals is evaluated, and this permits theutilization of a considerably simpler signal receiver since only thepresence of an audible signal, rather than the repetition rate thereof,need be evaluated. Therefore, the evaluation time associated withreceived signals is considerably decreased relative to prior artsystems.

Since the call number transmitter may be in one of several possibleswitching states, depending upon the state of the connectionestablishment, and the number of digits transferred from the digitstorage means to the connection line in each particular case, aplurality of criteria are available because of the switching states ofthe signal receiver and the call number transmitter that may be employedto control the call number transmitter and to effect release of theconnection system. There thereby results a decrease in the time periodassociated with transmission of the call number and seizure of thecentral systems for establishment of the connection. A correspondingdecrease in the cost of the telephone system is thereby provided, andunnecessary delays for subscribers associated with the system areeliminated.

BRIEF DESCRlPTlON OF THE DRAWlNGS FIG. ll shows the connection between asubscriber station associated with a subscriber installation havingextension stations and a central call number transmitter, and asubscriber station connected to a public telephone system;

FIG. 2 shows the switching circuit associated with the subscriberinstallation shown in FlG. ll, according to the invention.

DETAILED DESClRlPTlON OE THE INVENTION FIG. ll shows the connectionbetween subscriber stations TNll and TN2. Subscriber station TNT isassociated with a subscriber installation having a plurality ofextension stations, and is connected by subscriber circuit TSll, linefinder A511, and group selector stage GW to repeater Ue. Central callnumber transmitter RNG is associated with the subscriber installation,and is also connected to repeater Ue. The output of repeater Ue isconnected to trunlt relay repeater AUe, that is connected over a trunkline to subscriber circuit T52 of a public telephone exchange office.Line finder stage A52, first and second group selector stages lGW andllGW and line selector LW complete the connection to subscriber TNTConnection line DWN may be connected between second group selector stageCW and another subscriber installation (not shown) having extensionstations associated with a subscriber station capable of automaticdialing to establish connections to selected other subscribers. as wellas to associated extension stations. The subscriber connection shown isconventional and particulars thereof are therefore not described.

The subscriber installation having subscriber station TNT with extensionstations may therefore be connected by repeater Ue to coupling system itand thereby to central call number transmitter RNG. Sound receiver Te isconnected to central call number transmitter RNG for receipt of audiblesignals indicative of the state of the connection.

FIG. 2 shows the switching circuit according to the invention of asubscriber installation having extension stations for subscriber stationTN 1, with respect to repeater Ue, coupling system K, central callnumber transmitter RNG, and sound receiver Te. The disclosed switchingcircuit is described in relation to the establishment of an automaticconnection by central call number transmitter RNG.

When subscriber station TNl seizes repeater Ue, relay A of repeater U:is energized through hold contact in of relay TT. Additionally, couplingsystem K functions to actuate contacts K to the closed positions. Thus,subscriber station TNl seizes short call number storage means KSP, thatcomprises part of central call transmitter RNG, through contacts la anddw. As known in the prior art, the calling subscriber may dial anidentification or short call number that can be converted to the callnumber of the called subscriber. Thus, subscriber TNl may dial a shortcall number into storage means KSP consisting, for example, of twodigits. Converter UW is connected to the output thereof and converts theshort call number to the corresponding call number of the calledsubscriber, consisting, for example, of n digits, for storage in callnumber storage means SP. The stored call number may then be transmittedover pulse relay J in the form of successive pulse series, assuming eachdigit of the call number comprises a predetermined pulse series.

Call number storage means SP thus comprises individual storage sections1 through n, corresponding to the number of individual digits comprisingthe call number, and the state of each of individual storage sections 1through n determines the derived switching criteria. For example, ifdigit n is stored in individual storage section n, contacts In, 2n, andBr: will be actuated to the closed positions.

Further, contact dw functions to apply additional digits (n+1 through 2:to supplementary storage means DSP after the short call number isdialed, if desired. This is accomplished by a switching device (notshown), which actuates contact dw to the position wherein it completesthe connection to supplementary storage means DSP. The additional digitsmay then be used to automatically connect the calling subscriber to acalled subscriber having extension stations.

Thus, if connection line DWN connects a subscriber installation having asubscriber with extension stations to second line selector stage llGW, adirect connection thereto can be effected automatically.

When subscriber station TNl seizes repeater Ue, sound receiving relay Tis connected to receive audible signals through contacts d, k, 1], andlv (as shown), when contact in is closed. When digits l through ncomprising the call number are stored in the corresponding storagesections 1 through n of call number storage means SP, contact In isactuated by storage section n to the closed position to complete theelectrical connection to sound receiving relay T. Sounding receivingrelay T may receive audible signals transmitted over the connection pathshown. Upon receipt of an audible signal, sound receiving relay T isenergized and actuates contact 1! to the closed position to therebyenergize start relay ST over winding STl thereof. This causes contact3st to be actuated to the closed position, to thereby cause the callnumber stored in call number storage means SP to be applied to pulserelay J in sequential manner (digits 1 through n successively).

Pulse relay J is responsive to the sequence of pulse series stored incall number storage means SP to cause transmission of a correspondingpulse series sequence to the connection path or line. During the timeinterval that a pulse series is being applied to pulse relay J, contactlj functions to break the electrical connection to sound receiving relayT.

Contact I] is opened and contact 2] is closed in response to the lendingedges of pulses comprising the pulse series of each digit. When contact2/ is closed. it completes the electrical connection to delay relay Vand causes energization thereof thereby opening contact lv. Contact ljcloses and contact 2 opens in response to the trailing edges of thepulses. However, delay relay V functions to maintain contact lv in theopen position for a predetermined time period, so that the switchingcircuit can determine if the pulse comprises the terminal pulse of thepulse series associated with the digit being transmitted, or if it is tobe succeeded by additional pulse or pulses comprising the pulse seriesof the digit being transmitted. If the time interval between successivepulses is greater than said predetermined time period, it is indicativethat the pulse comprised the terminal pulse of the digit, and delayrelay V then functions to close contact lv, and the electricalconnection to signal receiving relay T is again completed. Thus, thetime interval between successive pulses of a given pulse series shouldbe less than the time period between successive pulse series. Further.contact I] may be adapted to efi'ect transmission of the digit beingapplied to pulse relay J to the connection line by conventional means(not shown). Therefore, sound receiving relay T can only be responsiveto signals received either prior to transmission of a pulse series, orduring the time interval between successively transmitted pulse series(digits). The former signal may be a dial tone indicative that a callconnection can be made, and the latter signal may be a busy signalindicative that the call connection cannot be completed.

Thus the first digit (l) stored in storage section 1 is transmitted inthe form of a first pulse series, independently of the repetition rateof the received audible signal, and upon completion of transmission ofthe first pulse series, the electrical circuit of the sound receivingrelay T is again completed because contacts iv and lj are then actuatedto the closed position. Relay ST is held in the energized state duringtransmission of the first pulse series to the connection line by holdwinding STll, the connection thereto being completed by closed contacts1:! and 2n, the latter being actuated to the closed position duringtransmission of the first pulse series to the connection line becausedigit n remains stored in storage section n. If the received audiblesignal was a dial tone, the remaining digits 2 through n are thentransmitted to the connection line.

However, assuming that an audible signal is applied to sound receivingrelay T within the time interval between transmission to the connectionline of the first and second pulse series (corresponding to the firstand second digits of the call number), it would be indicative of a busysignal. Since the digit stored in storage section 1 (digit 1) hasalready been transmitted to the connection line, contact I is closed.Then, when sound receiving relay T responds to receipt of the busysignal, contact 2! is also closed to complete the electrical connectionof relay Bl. This, in turn, causes actuation of contact lb to the closedposition, and completes the electrical connection between subscriberstation TN] and sound receiver Te, to cause energization of relay TT andthe consequent actuation of its contact In to the open position. Thusrelay A is deenergized and repeater Ue is switched out of connectionwith subscriber station TNl. Further, the connection between centralcall number transmitter RNG and repeater Ue, as well as the connectionpath established by transmission of the first digit is also broken.Therefore, repeater Ue and central call transmitter RNG are freed forseizure by other subscribers and new dialing operations can be initiatedusing this equipment.

Thus it is seen that in the above-described switching circuit accordingto the invention, the first digit of a call number is transmitted afterreceipt of an audible signal. in prior art telephone systems wherein abusy signal can be produced prior to transmission of the first digitwhile the preselection stage is seized, utilization of the switchingarrangement according to the invention (which does not provide for theevaluation of the repetition rate of received signals) would also causetransmission of the first digit. Then, after transmission of the firstdigit, the system (that is, prior art telephone systems) would bedisconnected since the busy signal would continue.

However, if a connection is established without receipt of a busysignal, sound receiving relay T would not be responsive to receivedsignals during the time intervals between successive dial signals to betransmitted. Notification of the call would be transmitted to the publictelephone system through the established connection path aftertransmission of the last dial signal. Sound receiving relay T then canno longer respond to received signals because the contents of storagesection n has been transferred, and contact In is therefore in the openposition.

Therefore, the switching circuit provides for the disconnection of thesystem under these conditions, by employing time transmitter system 26which responds to relay B to free the seized exchange systems if soundreceiving relay T is not energized prior to transmission of the firstdigit. Thus, time transmitter system is connected in a circuitcomprising holding contact 2st of start relay ST and contact 3n, thelatter being actuated to the closed position when the last digit n ofthe call number is stored in storage section n of call number storagemeans SP. Then, if sound receiving relay T is not energized (in responseto a received audible signal) start relay ST is not energized, andcontact 2." remains closed as shown in FIG. 2. After the elapsing of apredetermined time period, time transmitter system 20 is energized, andactuates its contact 120 to the closed position to complete theelectrical connection for relay winding Bll. This causes contact lb tobe actuated to the closed position, and to thereby effect release ofrepeater Ue, central call number transmitter RNG, sound receiver Te, andthe connection path, and these are then available for use by othersubscribers.

It may be desired to establish a connection between selected subscribersby employing call numbers having less than n digits. Therefore, callnumber storage means SP may be adapted such that the switching circuitis actuated to effect transmission of the call number when the lastdigit thereof is stored in its corresponding storage section. Thus, anappropriate switching system (not shown) may be employed that isresponsive to effect opening of contact In after the shortest callnumber desired to be used has been transmitted.

When a connection is established between the calling and calledsubscribers, conventional means (not shown) are operative to causecontact d to complete the connection between the called and callingsubscribers so that telephone communication may take place.

It will be evident that many changes could be made in the systems of theinvention without departure from the scope thereof. Accordingly, theinvention is not to be considered limited to the particular embodimentsdisclosed herein, but only by the scope of the appended claims. It istherefore intended by the appended claims to cover all suchmodifications and adaptations as fall within the true spirit and scopeof the invention.

We claim:

l. A telephone installation circuit arrangement for processing callconnection demands from calling (TNl) subscribers associated with anexchange system having call number transmitters (RNG) to automaticallyestablish connections to called subscribers, and associated signalreceivers (TE) to automatically supervise the operating state ofconnection systems associated with connection lines seized by callingsubscribers comprising:

storage means (SP) associated with the call number transmitters (RNG) tostore dialed call numbers comprising a plurality of successively dialeddigits I through n); first switching means (in) actuated in response tostorage of a complete dialed call number in the storage means (SP) toconnect the associated signal receiver (TE) to the seized connectionline during time intervals prior to transmission of the first digitthereto by the call number transmitter, and between transmission ofsuccessively dialed digits; evaluation means (V, ST, 20) to evaluate thestates of the storage means (SP) and the signal receiver upon receipt ofsignals by the latter to derive control information indicative of theoperating state of the connection system associated with the seizedconnection line; and connection means (T, B) responsive to derivedcontrol in formation to selectively initiate transmission of the callnumber to the seized connection line or effect release of the exchangesystem from the calling subscriber.

2. The telephone installation circuit arrangement recited in claim 1wherein the evaluation means comprises a time transmission system (26)responsive if no signal is received by said signal receiver associatedtherewith prior to transmission of the first digit of the call number tocontrol the connection means to effect release of the exchange systemfrom the calling system.

3. The telephone system circuit arrangement recited in claim 2 furthercomprising a short number converter to convert dialed short numbers tothe desired call number.

4. The telephone system circuit arrangement recited in claim 2 whereinsubscribers associated with the exchange have extension stations and acentral call number transmitter and signal receiver that may beselectively seized to establish connections to called subscribers.

5. The telephone system circuit arrangement recited in claim 2 whereinreceipt of a signal by the signal receiver during the time intervalbetween successive transmission of the first and second digit of callnumbers controls the connection means to effect release of the exchangesystem from the calling subscriber.

6. The telephone installation circuit recited in claim ll whereinreceipt of a dial tone by the signal receiver controls said connectionmeans to initiate transmission of the call number to the seizedconnection line after the complete dialed call number is stored in thestorage means.

